Urethane-based pressure sensitive adhesives

ABSTRACT

Non-silicone, urethane-based adhesives are disclosed which are prepared by the polymerization of reactive oligomers with the general formula X-A-B-A-X, where X is an ethylenically unsaturated group B is a unit free of silicone, and A is a urethane linkage. The adhesives are optically clear, self wetting and removable. Adhesive articles, including optical adhesive articles, may be prepared using the disclosed non-silicone urethane-based adhesives.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to the field of adhesives,specifically to the field of pressure sensitive adhesives that arenon-silicone and urethane-based.

BACKGROUND

Adhesives have been used for a variety of marking, holding, protecting,sealing and masking purposes. Adhesive tapes generally comprise abacking, or substrate, and an adhesive. One type of adhesive, a pressuresensitive adhesive, is particularly useful for many applications.

Pressure sensitive adhesives are well known to one of ordinary skill inthe art to possess certain properties at room temperature including thefollowing: (1) aggressive and permanent tack, (2) adherence with no morethan finger pressure, (3) sufficient ability to hold onto an adherend,and (4) sufficient cohesive strength to be removed cleanly from theadherend. Materials that have been found to function well as pressuresensitive adhesives are polymers designed and formulated to exhibit therequisite viscoelastic properties resulting in a desired balance oftack, peel adhesion, and shear strength. The most commonly used polymersfor preparation of pressure sensitive adhesives are natural rubber,synthetic rubbers (e.g., styrene/butadiene copolymers (SBR) andstyrene/isoprene/styrene (SIS) block copolymers), various (meth)acrylate(e.g., acrylate and methacrylate) copolymers and silicones. Each ofthese classes of materials has advantages and disadvantages.

SUMMARY

The need remains for adhesives with a range of different properties.Disclosed herein are urethane-based adhesives comprising a cured mixturecomprising at least one reactive oligomer with the general formulaX-A-B-A-X, wherein X comprises an ethylenically unsaturated group, Bcomprises a non-silicone unit with a number average molecular weight of5,000 grams/mole or greater, and A comprises a urethane linking group,wherein the adhesive is optically clear, self wetting and removable.

Also disclosed are curable reaction mixtures comprising at least oneX-A-B-A-X reactive oligomer, wherein X comprises an ethylenicallyunsaturated group, B comprises a non-silicone unit with a number averagemolecular weight of 5,000 grams/mole or greater, and A comprise aurethane linking group, and an initiator. In some embodiments, thecurable reaction mixture further comprises additional ethylenicallyunsaturated material.

Additionally, methods of preparing adhesives are disclosed, comprisingproviding a curable composition comprising at least one X-A-B-A-Xreactive oligomer, wherein X comprises an ethylenically unsaturatedgroup, B comprises a non-silicone unit with a number average molecularweight of 5,000 grams/mole or greater, and A comprises a urethanelinkage, and an initiator, and curing the curable composition.

Adhesive articles are disclosed comprising a pressure sensitive adhesivecomprising the cured reaction product of at least one X-A-B-A-X reactiveoligomer, wherein X comprises an ethylenically unsaturated group, Bcomprises a non-silicone unit with a number average molecular weight of5,000 grams/mole or greater, and A comprises a urethane linking group,wherein the adhesive is optically clear, self wetting and removable, anda substrate. A wide range of substrates are suitable for preparingadhesive articles.

DETAILED DESCRIPTION

The use of adhesives, especially pressure sensitive adhesives, in areassuch as the medical, electronic and optical industries is increasing.The requirements of these industries place additional demands upon thepressure sensitive adhesive beyond the traditional properties of tack,peel adhesion and shear strength. New classes of materials are desirableto meet the increasingly demanding performance requirements for pressuresensitive adhesives.

A class of non-silicone urethane-based adhesives, specifically pressuresensitive adhesives, are disclosed. These urethane-based adhesives areprepared from curable non-silicone, urethane-based reactive oligomers.The reactive oligomers contain free radically polymerizable groups. Insome embodiments the non-silicone urethane-based adhesives containpolyoxyalkylene (polyether) groups.

The non-silicone urethane-based adhesives, especially non-silicone,urethane-based pressure sensitive adhesives, prepared by the freeradical polymerization of non-silicone containing urethane-basedreactive oligomers, have a variety of silicone-like properties. Amongthese properties are optical clarity, self wetting and removability.

The term “adhesive” as used herein refers to polymeric compositionsuseful to adhere together two adherends. Examples of adhesives are heatactivated adhesives and pressure sensitive adhesives.

Heat activated adhesives are non-tacky at room temperature but becometacky and capable of bonding to a substrate at elevated temperatures.These adhesives usually have a Tg (glass transition temperature) ormelting point (Tm) above room temperature. When the temperature iselevated above the Tg or Tm, the storage modulus usually decreases andthe adhesive becomes tacky. Typically glass transition temperature (Tg)is measured using Differentially Scanning calorimetry (DSC).

Pressure sensitive adhesive compositions are well known to those ofordinary skill in the art to possess properties including the following:(1) aggressive and permanent tack, (2) adherence with no more thanfinger pressure, (3) sufficient ability to hold onto an adherend, and(4) sufficient cohesive strength to be cleanly removable from theadherend. Materials that have been found to function well as pressuresensitive adhesives are polymers designed and formulated to exhibit therequisite viscoelastic properties resulting in a desired balance oftack, peel adhesion, and shear holding power. Obtaining the properbalance of properties is not a simple process.

The term “non-silicone” as used herein refers to repeat units, tosegmented copolymers or units of segmented copolymers that are free ofsilicone units. The terms silicone or siloxane are used interchangeablyand refer to units with dialkyl or diaryl siloxane (—SiR₂O—) repeatingunits.

The term “urethane-based” as used herein refers to macromolecules thatare copolymers or segmented copolymers which contain at least oneurethane linkage. The urethane group has the general structure(—O—(CO)—NR—) where (CO) defines a carbonyl group C═O, and R is hydrogenor an alkyl group.

The term “segmented copolymer” refers to a copolymer of linked segments,each segment constitutes primarily a single structural unit or type ofrepeating unit. For example, a polyoxyalkylene segmented copolymer mayhave the following structure:

—CH₂CH₂(OCH₂CH₂)_(n)OCH₂CH₂-A-CH₂CH₂(OCH₂CH₂)_(n)OCH₂CH₂—

where A is the linkage between the 2 polyoxyalkylene segments, or it mayhave the following structure:

—CH₂CH₂(OCH₂CH₂)_(n)OCH₂CH₂-A-B—

where A is the linkage between the polyoxyalkylene segment and the Bsegment.

The term “reactive oligomer” as used herein refers to a macromoleculewhich contains terminal free radically polymerizable groups.“Urethane-based reactive oligomers” are macromolecules which containterminal free radical polymerizable groups and at least one urethanelinkage.

The term “alkyl” refers to a monovalent group that is a radical of analkane, which is a saturated hydrocarbon. The alkyl can be linear,branched, cyclic, or combinations thereof and typically has 1 to 20carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples ofalkyl groups include, but are not limited to, methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl,n-heptyl, n-octyl, and ethylhexyl.

The term “aryl” refers to a monovalent group that is aromatic andcarbocyclic. The aryl can have one to five rings that are connected toor fused to the aromatic ring. The other ring structures can bearomatic, non-aromatic, or combinations thereof. Examples of aryl groupsinclude, but are not limited to, phenyl, biphenyl, terphenyl, anthryl,naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl,pyrenyl, perylenyl, and fluorenyl.

The term “alkylene” refers to a divalent group that is a radical of analkane. The alkylene can be straight-chained, branched, cyclic, orcombinations thereof. The alkylene often has 1 to 20 carbon atoms. Insome embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of the alkylenecan be on the same carbon atom (i.e., an alkylidene) or on differentcarbon atoms.

The term “heteroalkylene” refers to a divalent group that includes atleast two alkylene groups connected by a thio, oxy, or —NR— where R isalkyl. The heteroalkylene can be linear, branched, cyclic, substitutedwith alkyl groups, or combinations thereof. Some heteroalkylenes arepoloxyyalkylenes where the heteroatom is oxygen such as for example,—CH₂CH₂(OCH₂CH₂)_(n)OCH₂CH₂—.

The term “arylene” refers to a divalent group that is carbocyclic andaromatic. The group has one to five rings that are connected, fused, orcombinations thereof. The other rings can be aromatic, non-aromatic, orcombinations thereof. In some embodiments, the arylene group has up to 5rings, up to 4 rings, up to 3 rings, up to 2 rings, or one aromaticring. For example, the arylene group can be phenylene.

The term “heteroarylene” refers to a divalent group that is carbocyclicand aromatic and contains heteroatoms such as sulfur, oxygen, nitrogenor halogens such as fluorine, chlorine, bromine or iodine.

The term “aralkylene” refers to a divalent group of formula—R^(a)—Ar^(a)— where R^(a) is an alkylene and Ar^(a) is an arylene(i.e., an alkylene is bonded to an arylene).

The term “(meth)acrylate” refers to monomeric acrylic or methacrylicesters of alcohols. Acrylate and methacrylate monomers are referred tocollectively herein as “(meth)acrylate” monomers.

The terms “free radically polymerizable” and “ethylenically unsaturated”are used interchangeably and refer to a reactive group which contains acarbon-carbon double bond which is able to be polymerized via a freeradical polymerization mechanism.

Unless otherwise indicated, “optically clear” refers to an adhesive orarticle that has a high light transmittance over at least a portion ofthe visible light spectrum (about 400 to about 700 nm), and thatexhibits low haze.

Unless otherwise indicated, “self wetting” refers to an adhesive whichis very soft and conformable and is able to be applied with very lowlamination pressure. Such adhesives exhibit spontaneous wet out tosurfaces.

Unless otherwise indicated, “removable” refers to an adhesive that hasrelatively low initial adhesion (permitting temporary removability fromand repositionability on a substrate after application), with a buildingof adhesion over time (to form a sufficiently strong bond), but remains“removable” i.e. the adhesion does not build beyond the point where itis permanently cleanly removable from the substrate.

Urethane-based adhesives are prepared from curable non-siliconeurethane-based reactive oligomers. The reactive oligomers contain freeradically polymerizable groups. The non-silicone urethane-based reactiveoligomers of this disclosure have the general structure X-A-B-A-X. Inthis structure the B unit is a non-silicone group with a number averagemolecular weight of 5,000 grams/mole or greater, the A groups areurethane linkages, and the X groups are ethylenically unsaturatedgroups.

The reactive oligomers described by the formula X-A-B-A-X may be amixture of reactive oligomers. The mixture of reactive oligomers mayinclude reactive oligomers which have a functionality of less than 2.These oligomers can be described by the general structure X-A-B—Y whereX, A, and B are as previously described and Y is a group that is notfree radically polymerizable and may or may not contain a urethanelinkage to the B unit. An example of a Y group is a hydroxyl (—OH) groupwhich could be the unreacted remnant from a HO—B—OH precursor. Thepresence of X-A-B—Y components along with the X-A-B-A-X components cangive a branched polymer when the mixture is polymerized because theunreactive Y groups do not become part of polymer backbone.

This branching, due to the use of monomers that are not completelydifunctional, is a common feature in many polyurethane adhesives becauseuntil recently, purely difunctional diols of high molecular weight werenot available. In the adhesives of the present disclosure, thisbranching, when present, does not produce undesirable properties, butrather may even be desirable. For example, branching may assist inproducing adhesives which have the desirable silicone-like propertiessuch as self wetting.

The X-A-B-A-X reactive oligomers may be prepared, for example, by thereaction of a hydroxyl-functional precursor of general formula HO—B—OHwith 2 equivalents of an isocyanate-functional precursor of the generalformula Z—X, where the Z group is isocyanate-functional and the X groupsare ethylenically unsaturated groups. The isocyanate functionality ofthe Z group reacts with a hydroxyl group of the polyol to form theurethane linkage.

A wide variety of HO—B—OH precursors may be used. The HO—B—OH may bepolyol or it may be a hydroxyl-capped prepolymer such as a polyurethane,polyester, polyamide, or polyurea prepolymer.

Examples of useful polyols include, but are not limited to, polyesterpolyols (e.g., lactone polyols) and the alkylene oxide (e.g., ethyleneoxide; 1,2-epoxypropane; 1,2-epoxybutane; 2,3-epoxybutane; isobutyleneoxide; and epichlorohydrin) adducts thereof, polyether polyols (e.g.,polyoxyalkylene polyols, such as polypropylene oxide polyols,polyethylene oxide polyols, polypropylene oxide polyethylene oxidecopolymer polyols, and polyoxytetramethylene polyols;polyoxycycloalkylene polyols; polythioethers; and alkylene oxide adductsthereof), polyalkylene polyols, mixtures thereof, and copolymerstherefrom. Polyoxyalkylene polyols are particularly useful.

When copolymers are used, chemically similar repeating units may berandomly distributed throughout the copolymer or in the form of blocksin the copolymer. Similarly, chemically similar repeating units may bearranged in any suitable order within the copolymer. For example,oxyalkylene repeating units may be internal or terminal units within acopolymer. The oxyalkylene repeating units may be randomly distributedor in the form of blocks within a copolymer. One example of a copolymercontaining oxyalkylene repeating units is a polyoxyalkylene-cappedpolyoxyalkylene polyol (e.g., a polyoxyethylene-cappedpolyoxypropylene).

When higher molecular weight polyols (i.e., polyols having weightaverage molecular weights of at least about 2,000) are used, it is oftendesirable that the polyol component be “highly pure” (i.e., the polyolapproaches its theoretical functionality—e.g., 2.0 for diols, 3.0 fortriols, etc.). These highly pure polyols generally have a ratio ofpolyol molecular weight to weight % monol of at least about 800,typically at least about 1,000, and more typically at least about 1,500.For example, a 12,000 molecular weight polyol with 8 weight % monol hassuch a ratio of 1,500 (i.e., 12,000/8=1,500). Generally it is desirablethat the highly pure polyol contains about 8% by weight monol or less.

Generally, as the molecular weight of the polyol increases in thisembodiment, a higher proportion of monol may be present in the polyol.For example, polyols having molecular weights of about 3,000 or lessdesirably contain less than about 1% by weight of monols. Polyols havingmolecular weights of greater than about 3,000 to about 4,000 desirablycontain less than about 3% by weight of monols. Polyols having molecularweights of greater than about 4,000 to about 8,000 desirably containless than about 6% by weight of monols. Polyols having molecular weightsof greater than about 8,000 to about 12,000 desirably contain less thanabout 8% by weight of monols.

Examples of highly pure polyols include those available from LyondellChemical Company of Houston, Tex., under the trade designation, ACCLAIM,and certain of those under the trade designation, ARCOL.

Where HO—B—OH is a hydroxyl-capped prepolymer, a wide variety ofprecursor molecules can be used to produce the desired HO—B—OHprepolymer. For example, the reaction of polyols with less thanstoichiometric amounts of diisocyanates can produce a hydroxyl-cappedpolyurethane prepolymer. Examples of suitable diisocyanates include, butare not limited to, aromatic diisocyanates, such as 2,6-toluenediisocyanate, 2,5-toluene diisocyanate, 2,4-toluene diisocyanate,m-phenylene diisocyanate, p-phenylene diisocyanate, methylenebis(o-chlorophenyl diisocyanate),methylenediphenylene-4,4′-diisocyanate, polycarbodiimide-modifiedmethylenediphenylene diisocyanate, (4,4′-diisocyanato-3,3′,5,5′-tetraethyl) biphenylmethane,4,4′-diisocyanato-3,3′-dimethoxybiphenyl, 5-chloro-2,4-toluenediisocyanate, 1-chloromethyl-2,4-diisocyanato benzene,aromatic-aliphatic diisocyanates such as m-xylylene diisocyanate,tetramethyl-m-xylylene diisocyanate, aliphatic diisocyanates, such as1,4-diisocyanatobutane, 1,6-diisocyanatohexane,1,12-diisocyanatododecane, 2-methyl-1,5diisocyanatopentane, andcycloaliphatic diisocyanates such asmethylene-dicyclohexylene-4,4′-diisocyanate, and3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl isocyanate (isophoronediisocyanate).

An example of the synthesis of a HO—B—OH prepolymer is shown in ReactionScheme 1 (where (CO) represents a carbonyl group C═O) below:

HO—R¹—OH+OCN—R²—NCO→HO—R¹—O—[(CO)N—R²—N(CO)O—R¹—O—]_(n)H   ReactionScheme 1

where n is one or greater, depending upon the ratio of polyol todiisocyanate, for example, when the ratio is 2:1, n is 1. Similarreactions between polyols and dicarboxylic acids or dianhydrides cangive HO—B—OH prepolymers with ester linking groups.

To prepare the non-silicone urethane-based reactive oligomers X-A-B-A-X,typically the HO—B—OH compounds are capped with an X—Z compound. The Zgroup of the X—Z compound is an isocyanate group and the X group is anethylenically unsaturated group (i.e. a carbon-carbon double bond) andis linked to the Z group. The link between the X and Z groups may be asingle bond or it may be a linking group. The linking group may be analkylene group, a heteroalkylene group, an arylene group, aheteroarylene group, an aralkylene group, or a combination thereof.

Examples of X—Z compounds include a variety of different isocyanato(meth)acrylates such as isocyanatoethyl methacrylate, andm-isopropenyl-α,α-dimethyl benzyl isocyanate. An example of thesynthesis of a X-A-B-A-X reactive oligomer is shown in Reaction Scheme 2below:

HO—B—OH+2OCN—R³—X→X—R³—HN(CO)O—B—O(CO)NH—R³—X   Reaction Scheme 2

The B unit in the X-A-B-A-X reactive oligomer is a non-silicone groupthat may contain a variety of groups such as urea groups, amide groups,ether groups, carbonyl groups, ester groups, alkylene groups,heteroalkylene groups, arylene groups, heteroarylene groups, aralkylenegroups, or combinations thereof. The B unit may also have a variety ofmolecular weights, depending upon the desired properties of the adhesiveformed from the reactive oligomer. Generally, the B unit has a numberaverage molecular weight of 5,000 grams/mole or greater. In someembodiments, the B unit is a heteroalkylene group.

A variety of X-A-B-A-X curable non-silicone urethane-based reactiveoligomers are commercially available. For example, a urethane acrylateoligomer of weight average molecular weight in the range of 4,000-7,000g/mole is commercially available from Nihon Gosei Kagaku under the tradename “UV-6100B”. Also a variety of urethane oligomers are available fromSartomer Company, Exton, Pa. under the trade names “CN9018”, “CN9002”and “CN9004”.

Non-silicone urethane-based pressure sensitive adhesives may be preparedby polymerizing X-A-B-A-X reactive oligomers through the ethylenicallyunsaturated X groups to form polymers with adhesive properties. Thepolymers may contain only X-A-B-A-X reactive oligomers or they may becopolymers in which additional monomers or reactive oligomers areincorporated. As used herein, additional monomers or reactive oligomersare collectively referred to as ethylenically unsaturated materials.

Among the additional monomers useful for incorporation are monomerswhich contain ethylenically unsaturated groups and are thereforeco-reactive with the reactive oligomers. Examples of such monomersinclude (meth)acrylates, (meth)acrylamides, alpha-olefins, and vinylcompounds such as vinyl acids, acrylonitriles, vinyl esters, vinylethers, styrenes and ethylenically unsaturated oligomers. In someinstances more than one type of additional monomer may be used.

Examples of useful (meth)acrylates include alkyl (meth)acrylates,aromatic (meth)acrylates, and silicone acrylates. In applications inwhich it is desirable that the entire adhesive composition be siliconefree, silicone acrylates are generally not used. Alkyl (meth)acrylatemonomers are those in which the alkyl groups comprise 1 to about 20carbon atoms (e.g., from 3 to 18 carbon atoms). Suitable acrylatemonomers include, for example, methyl acrylate, ethyl acrylate, n-butylacrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate,iso-octyl acrylate, octadecyl acrylate, nonyl acrylate, decyl acrylate,and dodecyl acrylate. The corresponding methacrylates are useful aswell. An example of an aromatic (meth)acrylate is benzyl acrylate.

Examples of useful (meth)acrylamides, include acrylamide, methacrylamideand substituted (meth)acrylamides such as N,N-dimethyl acrylamide,N,N-dimethyl methacrylamide, N,N-dimethylaminopropyl methacrylamide,N,N-diethylaminopropyl methacrylamide. N,N-dimethylaminoethylacrylamide, N,N-dimethylaminoethyl methacrylamide, N,N-diethylaminoethylacrylamide, and N,N-diethylaminoethyl methacrylamide.

The alpha-olefins useful as additional monomers generally include thosewith 6 or greater carbon atoms. The alpha-olefins with fewer than 6carbon atoms tend to be too volatile for convenient handling underambient reaction conditions. Suitable alpha-olefins include, forexample, 1-hexene, 1-octene, 1-decene and the like.

Examples of useful vinyl compounds include: vinyl acids such as acrylicacid, itaconic acid, methacrylic acid; acrylonitriles such asacrylonitrile and methacrylonitrile; vinyl esters such as vinyl acetateand the vinyl esters of carboxylic acids such as neodecanoic,neononanoic, neopentanoic, 2-ethylhexanoic, or propionic acids; vinylethers such as alkyl vinyl ethers; and styrenes such as styrene or vinyltoluene. Other vinyl compounds that may be useful includeN-vinylcaprolactam, vinylidene chloride, N-vinyl pyrrolidone, N-vinylformamide, and maleic anhydride. For some uses, for example electronicapplications, it may be desirable to include vinyl compounds that arefree of acidic groups.

Examples of ethylenically unsaturated oligomers useful forcopolymerization with the urethane-based reactive oligomers include, forexample, ethylenically unsaturated silicone oligomers such as aredescribe in the PCT publication number WO 94/20583 and macromolecularmonomers with relatively high glass transition temperatures as describedin U.S. Pat. No. 4,554,324 (Husman et al.). In applications in which itis desirable that the entire adhesive composition be silicone free,silicone oligomers are generally not used.

The reaction mixture may also, if desired, contain one or morecrosslinking agents. A crosslinking agent is used to build the molecularweight and the strength of the copolymer. Generally, the crosslinkingagent is one that is copolymerized with the non-silicone containingurethane-based reactive oligomers and any optional monomers. Thecrosslinking agent may produce chemical crosslinks (e.g., covalent bondsor ionic bonds). Alternatively, it may produce thermally reversiblephysical crosslinks that result, for example, from the formation ofreinforcing domains due to phase separation of hard segments (i.e.,those having a Tg higher than room temperature, generally higher than70° C.) such as the styrene macromers of U.S. Pat. No. 4,554,324(Husman) and/or acid/base interactions (i.e., those involving functionalgroups within the same polymer or between polymers or between a polymerand an additive) such polymeric ionic crosslinking as described in WO99/42536. Suitable crosslinking agents are also disclosed in U.S. Pat.No. 4,737,559 (Kellen), U.S. Pat. No. 5,506,279 (Babu et al.), and U.S.Pat. No. 6,083,856 (Joseph et al.). The crosslinking agent can be aphotocrosslinking agent, which, upon exposure to ultraviolet radiation(e.g., radiation having a wavelength of about 250 nanometers to about400 nanometers), causes the copolymer to crosslink.

Examples of suitable crosslinking agents include, for example,multifunctional ethylenically unsaturated monomers. Such monomersinclude, for example, divinyl aromatics, divinyl ethers, multifunctionalmaleimides, multifunctional acrylates and methacrylates, and the like,and mixtures thereof. Particularly useful are divinyl aromatics such asdivinyl benzene and multifunctional (meth)acrylates. Multifunctional(meth)acrylates include tri(meth)acrylates and di(meth)acrylates (thatis, compounds comprising three or two (meth)acrylate groups). Typicallydi(meth)acrylate crosslinkers (that is, compounds comprising two(meth)acrylate groups) are used. Useful tri(meth)acrylates include, forexample, trimethylolpropane tri(meth)acrylate, propoxylatedtrimethylolpropane triacrylates, ethoxylated trimethylolpropanetriacrylates, tris(2-hydroxy ethyl)isocyanurate triacrylate, andpentaerythritol triacrylate. Useful di(meth)acrylates include, forexample, ethylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, alkoxylated 1,6-hexanediol diacrylates, tripropyleneglycol diacrylate, dipropylene glycol diacrylate, cyclohexane dimethanoldi(meth)acrylate, alkoxylated cyclohexane dimethanol diacrylates,ethoxylated bisphenol A di(meth)acrylates, neopentyl glycol diacrylate,polyethylene glycol di(meth)acrylates, polypropylene glycoldi(meth)acrylates, and urethane di(meth)acrylates.

The crosslinking agent is used in an effective amount, by which is meantan amount that is sufficient to cause crosslinking of the pressuresensitive adhesive to provide adequate cohesive strength to produce thedesired final adhesion properties to the substrate of interest.Generally, the crosslinking agent is used in an amount of about 0.1 partto about 10 parts, based on the total amount of monomers.

Generally the non-silicone urethane-based adhesives are pressuresensitive adhesives and have glass transition temperature (Tg) values ofroom temperature (approximately 20° C.) or below. In some embodimentsthe Tg of the non-silicone urethane-based adhesives are 0° C. or below,or even −10° C. or below.

The non-silicone urethane-based adhesives can be made by solventprocesses, solventless processes (e.g., continuous solventless processesor polymerization on a surface or in a mold) or by a combination ofthese methods.

Some of the processes suitable for the preparation of the non-siliconeurethane-based adhesives include the free radical polymerization ofnon-silicone urethane-based reactive oligomers with optionalethylenically unsaturated materials in a reactor to form thenon-silicone urethane-based adhesive. The non-silicone urethane-basedadhesive can then be removed from the reaction vessel. Alternatively,the polymerization can be carried out by continuously mixing thereactants and depositing the reactants on a surface (e.g., release lineror substrate) or into a mold and polymerizing the mixture in place.

In some embodiments, it has been found convenient to deposit a mixtureof the non-silicone urethane-based reactive oligomer, additionalmonomers if desired, and initiator onto a surface, activate theinitiator and cure the adhesive on the surface. The mixture may or maynot contain a solvent. If solvent is used, the cured adhesive istypically dried to remove the solvent.

The initiator may be either a thermal initiator or a photoinitiator.Suitable thermal free radical initiators which may be utilized include,but are not limited to, those selected from azo compounds, such as2,2′-azobis(isobutyronitrile); hydroperoxides, such as tert-butylhydroperoxide; and, peroxides, such as benzoyl peroxide andcyclohexanone peroxide. Photoinitiators which are useful include, butare not limited to, those selected from benzoin ethers, such as benzoinmethyl ether or benzoin isopropyl ether; substituted benzoin ethers,such as anisole methyl ether; substituted acetophenones, such as2,2-diethoxyacetophenone and 2,2-dimethoxy-2-phenyl acetophenone;substituted alpha-ketols, such as 2-methyl-2-hydroxy propiophenone;aromatic sulfonyl chlorides, such as 2-naphthalene sulfonyl chloride;and, photoactive oximes, such as1-phenyl-1,2-propanedione-2-(ethoxycarbonyl)oxime or benzophenonederivatives. Benzophenone derivatives and methods for making them arewell known in the art, and are described in, for example, U.S. Pat. No.6,207,727 (Beck et al.). Exemplary benzophenone derivatives includesymmetrical benzophenones (e.g., benzophenone,4,4′-dimethoxybenzophenone, 4,4′-diphenoxybenzophenone,4,4′-diphenylbenzophenone, 4,4′-dimethylbenzophenone,4,4-dichlorobenzophenone); asymmetric benzophenones (e.g.,chlorobenzophenone, ethylbenzophenone, benzoylbenzophenone,bromobenzophenone); and free-radically polymerizable benzophenones(e.g., acryloxyethoxybenzophenone). Benzophenone itself is inexpensive,and may be preferable if cost is a factor. Copolymerizable benzophenonesmay be useful if residual odor or volatiles are a concern, and may bepreferable for those applications as they become covalently incorporatedinto the composition during cure. Examples of useful copolymerizablephotoinitiators are disclosed, for example, in U.S. Pat. No. 6,369,123(Stark et al.), U.S. Pat. No. 5,407,971 (Everaerts et al.), and U.S.Pat. No. 4,737,559 (Kellen et al.). The copolymerizablephotocrosslinking agents either generate free radicals directly orabstract hydrogen abstraction atoms to generate free radicals. Examplesof hydrogen abstraction type photocrosslinkers include, for example,those based on benzophenones, acetophenones, anthraquinones, and thelike. Examples of suitable copolymerizable hydrogen abstractioncrosslinking compounds include mono-ethylenically unsaturated aromaticketone monomers free of orthoaromatic hydroxyl groups. Examples ofsuitable free-radical generating copolymerizable crosslinking agentsinclude but are not limited to those selected from the group consistingof 4-acryloxybenzophenone (ABP), para-acryloxyethoxybenophenone, andpara-N-(methacryloxyethyl)-carbamoylethoxybenophenone. For both thermal-and radiation-induced polymerizations, the initiator is present in anamount of about 0.05% to about 5.0% by weight based upon the totalweight of the monomers.

In addition to the reactants, optional property modifying additives canbe mixed with the reactive oligomers and optional other monomersprovided that they do not interfere with the polymerization reaction.Typical property modifiers include tackifying agents (tackifiers) andplasticizing agents (plasticizers) to modify the adhesive performance ofthe formed adhesive composition. If used, the tackifiers andplasticizers are generally present in amounts ranging from about 5% toabout 55% by weight, about 10 to about 45% by weight or even from about10% to about 35% by weight.

Useful tackifiers and plasticizers are those conventionally used in theadhesive arts. Examples of suitable tackifying resins include terpenephenolics, alpha methyl styrene resins, rosin derived tackifiers,monomeric alcohols, oligomeric alcohols, oligomeric glycols, andmixtures thereof. Examples of useful plasticizing resins include terpenephenolics, rosin derived plasticizers, polyglycols and mixtures thereof.In some embodiments the plasticizer is isopropyl myristate or apolypropylene glycol.

The formed polymer composition may also be blended with additionalpressure sensitive adhesive polymers to modify the properties of thecomposition. In some embodiments an acidic pressure sensitive adhesive,such as an acidic (meth)acrylate pressure sensitive adhesive, is blendedto form an acid-base interaction with the urethane groups on thenon-silicone urethane-based adhesive copolymer. This acid-baseinteraction between the polymers is a Lewis acid-base type interaction.Lewis acid-base type interactions require that one component be anelectron acceptor (acid) and the other an electron donor (base). Theelectron donor provides an unshared pair of electrons and the electronacceptor furnishes an orbital system that can accommodate the additionalunshared pair of electrons. In this instance acid groups, typicallycarboxylic acid groups on the added (meth)acrylate pressure sensitiveadhesive polymer interact with the unshared electron pairs of theurethane groups.

Examples of suitable (meth)acrylate pressure sensitive adhesives include(meth)acrylate copolymers prepared from alkyl (meth)acrylate monomersand may contain additional monomers such as vinyl monomers. Examples ofsuch alkyl (meth)acrylate monomers are those in which the alkyl groupscomprise from about 4 carbon atoms to about 12 carbon atoms and include,but are not limited to, n-butyl acrylate, 2-ethylhexyl acrylate,isooctyl acrylate, isononyl acrylate, isodecyl, acrylate, and mixturesthereof. Optionally, other vinyl monomers and alkyl (meth)acrylatemonomers which, as homopolymers, have a Tg greater than 0° C., such asmethyl acrylate, methyl methacrylate, isobornyl acrylate, vinyl acetate,styrene, and the like, may be utilized in conjunction with one or moreof the low Tg alkyl (meth)acrylate monomers and copolymerizable acidicmonomers, provided that the Tg of the resultant (meth)acrylate copolymeris less than about 0° C.

When the (meth)acrylate pressure sensitive adhesive is an acidiccopolymer, the acidic (meth)acrylate copolymers typically are derivedfrom acidic monomers comprising about 2% by weight to about 30% byweight, or about 2% by weight to about 15% by weight, of acopolymerizable acidic monomer. Examples of useful acidic monomersinclude (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid,fumaric acid, and the like.

When used, the added pressure sensitive adhesive may be used in anysuitable amount to achieve the desired properties of the composition.For example, the added pressure sensitive adhesive may be added inamounts of from about 5 to about 60 weight % of the composition.

In addition, other property modifiers, such as fillers, may be added ifdesired, provided that if and when incorporated, such additives are notdetrimental to the properties desired in the final composition. Fillers,such as fumed silica, fibers (e.g., glass, metal, inorganic, or organicfibers), carbon black, glass or ceramic beads/bubbles, particles (e.g.,metal, inorganic, or organic particles), polyaramids (e.g., thoseavailable from DuPont Chemical Company; Wilmington, Del. under the tradedesignation, KEVLAR), and the like which can be added in amounts up toabout 30% by weight. Other additives such as dyes, inert fluids (e.g.,hydrocarbon oils), pigments, flame retardants, stabilizers,antioxidants, compatibilizers, antimicrobial agents (e.g., zinc oxide),electrical conductors, thermal conductors (e.g., aluminum oxide, boronnitride, aluminum nitride, and nickel particles), and the like can beblended into these systems in amounts of generally from about 1 to about50 percent by total volume of the composition.

The adhesives formed by the polymerization of the non-siliconeurethane-based reactive oligomers may be pressure sensitive adhesives orheat activated adhesives. Generally pressure sensitive adhesives areformed. These pressure sensitive adhesives are useful in a wide array ofapplications.

The use of reactive oligomers instead of low molecular weight monomersto generate the pressure sensitive adhesive polymers results in polymersthat are free of volatile unreacted materials and other low molecularweight impurities after polymerization. Residual monomers and lowmolecular weight impurities may be problematic in certain applications,such as medical and electronic applications. In medical and electronicapplications, residual monomers and impurities may cause, for example,undesirable odor or potential contamination of substrates/articles(e.g., hard disk drives) in which they are in contact. In addition, theuse of reactive oligomers which are free of silicone is desirable incertain industries, such as the electronics industry, where siliconecontamination is a concern.

The adhesive, or the reactive mixture which upon polymerization formsthe adhesive, may be coated onto a surface to form a wide variety ofadhesive articles. For example, the adhesive can be applied to films orsheeting products (e.g., decorative, reflective, and graphical),labelstock, tape backings (e.g., polymeric films, metal films, paper,creped paper, foams, and the like), release liners, and the like. Thesubstrate can be any suitable type of material depending on the desiredapplication.

The adhesive can be formed into a film or coating by either continuousor batch processes. An example of a batch process is the placement of aportion of the adhesive between a substrate to which the film or coatingis to be adhered and a surface capable of releasing the adhesive film orcoating to form a composite structure. The composite structure can thenbe compressed at a sufficient temperature and pressure to form aadhesive coating or film of a desired thickness after cooling.Alternatively, the adhesive can be compressed between two releasesurfaces and cooled to form an adhesive transfer tape useful inlaminating applications.

Continuous forming methods include drawing the adhesive out of a filmdie and subsequently contacting the drawn adhesive to a moving plasticweb or other suitable substrate. A related continuous method involvesextruding the adhesive and a coextruded backing material from a film dieand cooling the layered product to form an adhesive tape. Othercontinuous forming methods involve directly contacting the adhesive to arapidly moving plastic web or other suitable preformed substrate. Usingthis method, the adhesive is applied to the moving preformed web using adie having flexible die lips, such as a rotary rod die. After forming byany of these continuous methods, the adhesive films or layers can besolidified by quenching using both direct methods (e.g., chill rolls orwater baths) and indirect methods (e.g., air or gas impingement).

Adhesives can also be coated using a solvent-based method. For example,the adhesive can be coated by such methods as knife coating, rollcoating, gravure coating, rod coating, curtain coating, and air knifecoating. The adhesive mixture may also be printed by known methods suchas screen printing or inkjet printing. The coated solvent-based adhesiveis then dried to remove the solvent. Typically, the coated solvent-basedadhesive is subjected to elevated temperatures, such as those suppliedby an oven, to expedite drying of the adhesive.

In some embodiments it may be desirable to impart a microstructuredsurface to one or both major surfaces of the adhesive. It may bedesirable to have a microstructured surface on at least one surface ofthe adhesive to aid air egress during lamination. If it is desired tohave a microstructured surface on one or both surfaces of the adhesivelayer, the adhesive coating or layer may be placed on a tool or a linercontaining microstructuring. Either the adhesive or the reactive mixturewhich upon polymerization forms the adhesive, may be placed on a tool ora liner. The liner or tool can then be removed to expose an adhesivelayer having a microstructured surface. Upon lamination, themicrostructuring on the surface of the adhesive may disappear over timeas the adhesive wets the surface. This is particularly desirable wherethe adhesive is used in an optical construction where residualmicrostructuring could interfere with the optical properties of theoptical construction.

The thickness of the adhesive layer tends to be at least about 1micrometer, at least 5 micrometers, at least 10 micrometers, at least 15micrometers, or at least 20 micrometers. The thickness is often nogreater than about 200 micrometers, no greater than about 175micrometers, no greater than about 150 micrometers, or no greater thanabout 125 micrometers. For example, the thickness can be 1 to 200micrometers, 5 to 100 micrometers, 10 to 50 micrometers, 20 to 50micrometers, or 1 to 15 micrometers.

The pressure sensitive adhesives are typically optically clear.Optically clear adhesives may be used to make a wide array of opticalarticles. Such articles may include an optical film, a substrate orboth. Such uses include information displays, window coverings, graphicarticles and the like.

Articles are provided that include an optical film and a pressuresensitive adhesive layer adjacent to at least one major surface of theoptical film. The articles can further include another substrate (e.g.,permanently or temporarily attached to the pressure sensitive adhesivelayer), another adhesive layer, or a combination thereof. As usedherein, the term “adjacent” can be used to refer to two layers that arein direct contact or that are separated by one or more layers. Often,adjacent layers are in direct contact.

In some embodiments, the resulting articles can be optical elements orcan be used to prepare optical elements. As used herein, the term“optical element” refers to an article that has an optical effect oroptical application. The optical elements can be used, for example, inelectronic displays, architectural applications, transportationapplications, projection applications, photonics applications, andgraphics applications. Suitable optical elements include, but are notlimited to, screens or displays, cathode ray tubes, polarizers,reflectors, and the like.

Any suitable optical film can be used in the articles. As used herein,the term “optical film” refers to a film that can be used to produce anoptical effect. The optical films are typically polymer-containing filmsthat can be a single layer or multiple layers. The optical films areflexible and can be of any suitable thickness. The optical films oftenare at least partially transmissive, reflective, antireflective,polarizing, optically clear, or diffusive with respect to somewavelengths of the electromagnetic spectrum (e.g., wavelengths in thevisible ultraviolet, or infrared regions of the electromagneticspectrum). Exemplary optical films include, but are not limited to,visible mirror films, color mirror films, solar reflective films,infrared reflective films, ultraviolet reflective films, reflectivepolarizer films such as a brightness enhancement films and dualbrightness enhancement films, absorptive polarizer films, opticallyclear films, tinted films, privacy films such as light-collimatingfilms, and antireflective films.

In some embodiments the optical film has a coating. In general, coatingsare used to enhance the function of the film or provide additionalfunctionality to the film. Examples of coatings include, for example,hardcoats, anti-fog coatings, anti-scratch coatings, privacy coatings ora combination thereof. Coatings such as hardcoats, anti-fog coatings,and anti-scratch coatings that provide enhanced durability, aredesirable in applications such as, for example, touch screen sensors,display screens, graphics applications and the like. Examples of privacycoatings include, for example, blurry or hazy coatings to give obscuredviewing or louvered films to limit the viewing angle.

Some optical films have multiple layers such as multiple layers ofpolymer-containing materials (e.g., polymers with or without dyes) ormultiple layers of metal-containing material and polymeric materials.Some optical films have alternating layers of polymeric material withdifferent indexes of refraction. Other optical films have alternatingpolymeric layers and metal-containing layers. Exemplary optical filmsare described in the following patents: U.S. Pat. No. 6,049,419(Wheatley et al.); U.S. Pat. No. 5,223,465 (Wheatley et al.); U.S. Pat.No. 5,882,774 (Jonza et al.); U.S. Pat. No. 6,049,419 (Wheatley et al.);U.S. Pat. No. RE 34,605 (Schrenk et al.); U.S. Pat. No. 5,579,162(Bjornard et al.), and U.S. Pat. No. 5,360,659 (Arends et al.).

The substrate included in the article can contain polymeric materials,glass materials, ceramic materials, metal-containing materials (e.g.,metals or metal oxides), or a combination thereof. The substrate caninclude multiple layers of material such as a support layer, a primerlayer, a hard coat layer, a decorative design, and the like. Thesubstrate can be permanently or temporarily attached to an adhesivelayer. For example, a release liner can be temporarily attached and thenremoved for attachment of the adhesive layer to another substrate.

The substrate can have a variety of functions such as, for example,providing flexibility, rigidity, strength or support, reflectivity,antireflectivity, polarization, or transmissivity (e.g., selective withrespect to different wavelengths). That is, the substrate can beflexible or rigid; reflective or non-reflective; visibly clear, coloredbut transmissive, or opaque (e.g., not transmissive); and polarizing ornon-polarizing.

Exemplary substrates include, but are not limited to, the outer surfaceof an electronic display such as liquid crystal display or a cathode raytube, the outer surface of a window or glazing, the outer surface of anoptical component such as a reflector, polarizer, diffraction grating,mirror, or lens, another film such as a decorative film or anotheroptical film, or the like.

Representative examples of polymeric substrates include those thatcontain polycarbonates, polyesters (e.g., polyethylene terephthalatesand polyethylene naphthalates), polyurethanes, poly(meth)acrylates(e.g., polymethyl methacrylates), polyvinyl alcohols, polyolefins suchas polyethylenes and polypropylenes, polyvinyl chlorides, polyimides,cellulose triacetates, acrylonitrile-butadiene-styrene copolymers, andthe like.

In other embodiments, the substrate is a release liner. Any suitablerelease liner can be used. Exemplary release liners include thoseprepared from paper (e.g., Kraft paper) or polymeric material (e.g.,polyolefins such as polyethylene or polypropylene, ethylene vinylacetate, polyurethanes, polyesters such as polyethylene terephthalate,and the like). At least some release liners are coated with a layer of arelease agent such as a silicone-containing material or afluorocarbon-containing material. Exemplary release liners include, butare not limited to, liners commercially available from CP Film(Martinsville, Va.) under the trade designation “T-30” and “T-10” thathave a silicone release coating on polyethylene terephthalate film. Theliner can have a microstructure on its surface that is imparted to theadhesive to form a microstructure on the surface of the adhesive layer.The liner can then be removed to expose an adhesive layer having amicrostructured surface.

The release liner can be removed to adhere the optical film to anothersubstrate (i.e., removal of the release liner exposes a surface of anadhesive layer that subsequently can be bonded to another substratesurface).

The adhesives are self wetting and removable. The adhesives exhibitgreat conformability permitting them to spontaneously wet outsubstrates. The surface characteristics also permit the adhesives to bebonded and removed from the substrate repeatedly for repositioning orreworking. The strong cohesive strength of the adhesives gives themstructural integrity limiting cold flow and giving elevated temperatureresistance in addition to permanent removability. In some embodimentsthe initial removability of an adhesive coated article bonded to a glasssubstrate, as measured by the 90° Peel Adhesion test described in theExamples section below, is no greater than 2.9 Newtons/decimeter (75grams per inch). Upon aging for one week at room temperature theremovability, as measured by the 90° Peel Adhesion test described in theExamples section below, is no more than 7.7 Newtons/decimeter (200 gramsper inch). In other embodiments, the removability after aging for atleast one week at room temperature, as measured by the 90° Peel Adhesiontest described in the Examples section below, is no more than 15.4Newtons/decimeter (400 grams per inch), 7.7 Newtons/decimeter (200 gramsper inch) or even 3.9 Newtons/decimeter (100 grams per inch).

Exemplary adhesive articles in which the self wetting and removabilityfeatures are especially important include, for example: large formatarticles such as graphic articles and protective films; and informationdisplay devices.

Large-format graphic articles or protective films typically include athin polymeric film backed by a pressure sensitive adhesive. Thesearticles may be difficult to handle and apply onto a surface of asubstrate. The large format article may be applied onto the surface of asubstrate by what is sometimes called a “wet” application process. Thewet application process involves spraying a liquid, typically awater/surfactant solution, onto the adhesive side of the large formatarticle, and optionally onto the substrate surface. The liquidtemporarily “detackifies” the pressure sensitive adhesive so theinstaller may handle, slide, and re-position the large format articleinto a desired position on the substrate surface. The liquid also allowsthe installer to pull the large format article apart if it sticks toitself or prematurely adheres to the surface of the substrate. Applyinga liquid to the adhesive may also improve the appearance of theinstalled large format article by providing a smooth, bubble freeappearance with good adhesion build on the surface of the substrate.

Examples of a large format protective films include window films such assolar control films, shatter protection films, decoration films and thelike. In some instances the film may be a multilayer film such as amultilayer IR film (i.e., an infrared reflecting film), such as amicrolayer film having selective transmissivity such as an opticallyclear but infrared reflecting film as described in U.S. Pat. No.5,360,659 (Arends et al.).

While the wet application process has been used successfully in manyinstances, it is a time consuming and messy process. A “dry” applicationprocess is generally desirable for installing large format graphicarticles. Adhesives that are self wetting and removable may be appliedwith a dry installation process. The articles are easily attached to alarge substrate because they are self wetting and yet they may be easilyremoved and repositioned as needed.

In other applications, such as information display devices, the wetapplication process cannot be used. Examples of information displaydevices include devices with a wide range of display area configurationsincluding liquid crystal displays, plasma displays, front and rearprojection displays, cathode ray tubes and signage. Such display areaconfigurations can be employed in a variety of portable and non-portableinformation display devices including personal digital assistants, cellphones, touch-sensitive screens, wrist watches, car navigation systems,global positioning systems, depth finders, calculators, electronicbooks, CD or DVD players, projection television screens, computermonitors, notebook computer displays, instrument gauges, instrumentpanel covers, signage such as graphic displays (including indoor andoutdoor graphics, bumper stickers, etc) reflective sheeting and thelike.

A wide variety of information display devices are in use, bothilluminated devices and non-illuminated devices. Many of these devicesutilize adhesive articles, such as adhesive coated films, as part oftheir construction. One adhesive article frequently used in informationdisplay devices is a protective film. Such films are frequently used oninformation display devices that are frequently handled or have exposedviewing surfaces.

In some embodiments, the adhesives of this disclosure may be used toattach such films to information display devices because the adhesiveshave the properties of optical clarity, self wetting and removability.The adhesive property of optical clarity permits the information to beviewed through the adhesive without interference. The features of selfwetting and removability permit the film to be easily applied to displaysurface, removed and reworked if needed during assembly and also removedand replaced during the working life of the information display device.

EXAMPLES

These examples are merely for illustrative purposes only and are notmeant to be limiting on the scope of the appended claims. All parts,percentages, ratios, etc. in the examples and the rest of thespecification are by weight, unless noted otherwise. Solvents and otherreagents used were obtained from Sigma-Aldrich Chemical Company;Milwaukee, Wis. unless otherwise noted.

Table of Abbreviations Abbreviation or Trade Designation Description VDMVinyl dimethyl azlactone Polyamine-1 Polyoxyalkylene polyamine ofapproximately 2,000 molecular weight, commercially available as“JEFFAMINE D-2000” from Huntsman, Houston, TX. Photoinitiator-1Photoinitiator “DAROCUR 4265” commercially. available from Ciba,Hawthorne, NY PET UV-primed polyester film of polyethylene terephthalateavailable under the trade name “Dupont 617” having a thickness of 127micrometers (5 mils) or 51 micrometers (2 mils) from Dupont TeijinFilms, Richmond, VA. Release Liner Polyester film of 51 micrometerthickness (2 mils) coated on one side with silicone release agent,commercially available from CP Film, Martinsville, VA as “T10 ReleaseLiner”. UBDA 8K Urea-based diamine of approximately 8,000 molecularweight, prepared as described in Synthesis Example 1. UBDA 12KUrea-based diamine of approximately 12,000 molecular weight, prepared asdescribed in Synthesis Example 2. UA-1 Urethane acrylate, aliphaticurethane oligomer commercially available from Sartomer Company Inc.,Exton PA as “CN9018”, with a published Tg = −56°C. UA-2 Urethaneacrylate, commercially available from Sartomer Company Inc., Exton PA as“CN9004”, with a published Tg = −76° C. UA-3 Urethane acrylate,commercially available from Sartomer Company Inc., Exton PA as “CN9002”,with a published Tg = −50.0° C. PSA-1 Pressure sensitive adhesivesolution, 20% solids by weight in ethyl acetate, of a copolymer PSA withan approximate ratio of monomers of 93/7 isoctyl acrylate/acrylic acidprepared as described in U.S. Pat. RE 24,906 (Ulrich). UA-4 Urethaneacrylate, commercially available from Sartomer Company Inc., Exton PA as“CN972”, with a published Tg = −47° C. UA-5 Urethane acrylate,commercially available from Sartomer Company Inc., Exton PA as “CN990”,with a published Tg = −37° C. UA-6 Urethane acrylate, commerciallyavailable from Sartomer Company Inc., Exton PA as “CN991”, with apublished Tg = +27° C. UA-7 Urethane acrylate, commercially availablefrom Sartomer Company Inc., Exton PA as “CN929”, with a published Tg =+43° C. TRPGDA Tripropylene glycol diacrylate

Test Methods 90° Peel Adhesion

Adhesive coatings of 51 micrometers (2 mils) thickness on 51 micrometer(2 mil) thick PET film were cut into 2.54 centimeter by 15 centimeterstrips. Each strip was then adhered to a 6.2 centimeter by 23 centimeterclean, solvent washed glass coupon using a 2-kilogram roller passed onceover the strip. The bonded assembly dwelled at room temperature forabout one minute and was tested for 90° peel adhesion using an IMASSslip/peel tester with a 90° peel testing assembly (Model SP2000,commercially available from Instrumentors Inc., Strongsville, Ohio) at arate of 2.3 meters/minute (90 inches/minute) over a five second datacollection time. Three samples were tested; the reported peel adhesionvalue is an average of the peel adhesion value from each of the threesamples. Data was measured in grams/inch width and converted to Newtonsper decimeter (N/dm).

Wet Out Test

Adhesive coatings of 51 micrometers (2 mils) thickness on 127 micrometer(5 mil) thick PET film were cut into sample squares of 12.7 by 12.7centimeters (5 by 5 inches). A 7.6 by 7.6 centimeter (3 by 3 inch)square was marked in the center of the backside of each sample square.The liner was removed from the sample square and one corner of thesample square was placed on the surface of an isopropanol-washed glasscoupon. The sample square was dropped onto the glass surface. The wetout time was measured using a stopwatch and was started when the wet outfront reached any part of the inner marked square and ended when theinner square was completely wet out. The wet out time was recorded, andis reported as the time (in seconds) per area wet out (in squarecentimeters).

Titration Method to Determine Molecular Weight

To determine the molecular weight of a synthesized UBDA, a measuredsample weight (about 4-6 grams) was placed in a jar and tetrahydrofuran(about 3 times the weight of the sample) was added with mixing to form auniform solution. A solution of the indicator bromophenol blue was addeduntil the color was a deep blue. With constant stirring, the samplesolution was titrated by adding 1.0 Normal HCl (aq) dropwise until acolor change from blue to yellow indicated that the endpoint wasreached. The endpoint volume of HCl titrated was recorded and themolecular weight was calculated.

SYNTHESIS EXAMPLES Synthesis Example 1 Preparation of UBDA 8K

A sample of Polyamine-1 (4 moles) was degassed under vacuum at 100° C.for 1 hour. Freshly ground diphenyl carbonate (3 moles) was added andthe mixture stirred to give a uniform mixture. The mixture was heated to160° C. for 3 hours under vacuum to remove phenol byproduct. Theresultant product was a urea chain extended diamine of approximately8,000 molecular weight (confirmed by titration, using the methoddescribed above).

Synthesis Example 2 Preparation of UBDA 12K

A sample of Polyamine-1 (6 moles) was reacted with a sample of diphenylcarbonate (5 moles) using the procedure described in Synthesis Example 1above. The resultant product was a urea chain extended diamine ofapproximately 12,000 molecular weight (confirmed by titration, using themethod described above).

Comparative Example C1

To a stirred sample of UBDA 8K (1 mole) was added slowly a sample of VDM(2 moles) at room temperature. The mixture was stirred and allowed toreact overnight. A sample of Photoinitiator-1 was added (0.5% byweight). The resultant mixture was cast between PET and a Release Lineron a knife die and marble bed hand spread coater to a thicknessappropriate for the test to be run on the sample and cured under lowintensity UV exposure using 40 watt, 350 nanometer bulbs for 10 minutes.Wet out testing to glass, 90° Peel adhesion to glass (initial and afteraging for 1 week at 70° C.) were carried out using the test methodsdescribed above. The results are presented in Table 1.

Comparative Example C2

To a stirred sample of UBDA 12K (1 mole) was added slowly a sample ofVDM (2 moles) at room temperature. The mixture was stirred and allowedto react overnight. A sample of Photoinitiator-1 was added (0.5% byweight). The resultant mixture was cast between PET and a Release Lineron a knife die and marble bed hand spread coater to a thicknessappropriate for the test to be run on the sample and cured under lowintensity UV exposure using 40 watt, 350 nanometer bulbs for 10 minutes.Wet out testing to glass, 90° Peel adhesion to glass (initial and afteraging for 1 week at 70° C.) were carried out using the test methodsdescribed above. The results are presented in Table 1.

Example 1

To a stirred sample of UA-1, Photoinitiator-1 was added (1.0% by weight)and the resultant mixture was cast between PET and a Release Liner on aknife die and marble bed hand spread coater to a thickness appropriatefor the test to be run on the sample and cured under high intensity UVexposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

Example 2

To a stirred sample of UA-2, Photoinitiator-1 was added (1.0% by weight)and the resultant mixture was cast between PET and a Release Liner on aknife die and marble bed hand spread coater to a thickness appropriatefor the test to be run on the sample and cured under high intensity UVexposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

Example 3

To a stirred sample of UA-3, Photoinitiator-1 was added (1.0% by weight)and the resultant mixture was cast between PET and a Release Liner on aknife die and marble bed hand spread coater to a thickness appropriatefor the test to be run on the sample and cured under high intensity UVexposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

Example 4

To a stirred sample of UA-1, IPM was added to 20% by weight,Photoinitiator-1 was added (1.0% by weight) and the resultant mixturewas cast between PET and a Release Liner on a knife die and marble bedhand spread coater to a thickness appropriate for the test to be run onthe sample and cured under high intensity UV exposure using Fusion 600Watt/in, D bulbs at 25 feet per minute (7.5 meters per minute) linespeed. Wet out testing to glass, 90° Peel adhesion to glass (initial andafter aging for 1 week at 70° C.) were carried out using the testmethods described above. The results are presented in Table 1.

Example 5

To a stirred sample of UA-1 (dissolved to in Ethyl Acetate to 80%solids), IPM was added to 25% by weight of total solids, TRPGDA wasadded to 15% by weight total solids, PSA-1 solution was added to 10% byweight of total solids, Photoinitiator-1 was added (1.0% by weight oftotal solids) and the resultant mixture was cast onto PET and dried for10 minutes at 70° C. to remove solvent. A release liner was laminatedonto the uncured coating and the sample was cured under high intensityUV exposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

Comparative Example C3

To a stirred sample of UA-4, Photoinitiator-1 was added (1.0% by weight)and the resultant mixture was cast between PET and a Release Liner on aknife die and marble bed hand spread coater to a thickness appropriatefor the test to be run on the sample and cured under high intensity UVexposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

Comparative Example C4

To a stirred sample of UA-5, Photoinitiator-1 was added (1.0% by weight)and the resultant mixture was cast between PET and a Release Liner on aknife die and marble bed hand spread coater to a thickness appropriatefor the test to be run on the sample and cured under high intensity UVexposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

Comparative Example C5

To a stirred sample of UA-6, Photoinitiator-1 was added (1.0% by weight)and the resultant mixture was cast between PET and a Release Liner on aknife die and marble bed hand spread coater to a thickness appropriatefor the test to be run on the sample and cured under high intensity UVexposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

Comparative Example C6

To a stirred sample of UA-7, Photoinitiator-1 was added (1.0% by weight)and the resultant mixture was cast between PET and a Release Liner on aknife die and marble bed hand spread coater to a thickness appropriatefor the test to be run on the sample and cured under high intensity UVexposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute (7.5meters per minute) line speed. Wet out testing to glass, 90° Peeladhesion to glass (initial and after aging for 1 week at 70° C.) werecarried out using the test methods described above. The results arepresented in Table 1.

TABLE 1 90° Peel Initial from Glass Wet-out 90° after aging to Peel1-week glass from 70° C. Speed Example (N/dm) (N/dm) (sec/cm²) C1 3.126.04 0.55 C2 5.17 12.74 1.39 1 13.90 34.20 0.31 2 0.73 1.16 0.10 3 1.382.12 0.16 4 4.13 10.22 0.17 5 2.23 5.40 0.14 C3 0.58 1.30 0.43 C4 <0.38— 0.78 C5 <0.38 — NW C6 <0.38 — NW NW = No wet out observed without theapplication of external pressure.

What is claimed is:
 1. An adhesive comprising a cured mixturecomprising: at least one X-A-B-A-X reactive oligomer, wherein Xcomprises an ethylenically unsaturated group, B comprises a non-siliconesegmented unit with a number average molecular weight of 5,000grams/mole or greater, and A comprises a urethane linking group, whereinthe X-A-B-A-X reactive oligomer is the reaction product of a HO—B—OHhydroxyl-capped prepolymer and an X—Z compound wherein Z is anisocyanate group and X is an ethylenically unsaturated group linked tothe Z group; and an initiator, wherein the adhesive is a pressuresensitive adhesive.
 2. The adhesive of claim 1, wherein the adhesive isa self-wetting and removable adhesive.
 3. The adhesive of claim 1,wherein cured mixture further comprises an ethylenically unsaturatedmaterial.
 4. The adhesive of claim 1, further comprising at least oneadditive, wherein the additive comprises a pressure sensitive adhesive,a plasticizing agent, a tackifying agent or a mixture thereof.
 5. Theadhesive of claim 4, comprising 5-60 weight % of added pressuresensitive adhesive and 5-55 weight % plasticizer.
 6. The adhesive ofclaim 5, wherein the plasticizer comprises isopropyl myristate orpolypropylene glygol.
 7. The adhesive of claim 6, wherein the addedpressure sensitive adhesive comprises a (meth)acrylate pressuresensitive adhesive.
 8. The adhesive of claim 7, wherein the addedpressure sensitive adhesive comprises an acid-containing (meth)acrylatepressure sensitive adhesive.
 9. A method of preparing an adhesivecomprising: providing a curable composition comprising: at least oneX-A-B-A-X reactive oligomer, wherein X comprises an ethylenicallyunsaturated group, B comprises a non-silicone unit with a number averagemolecular weight of 5,000 grams/mole or greater, and A comprises aurethane linkage; and an initiator; and curing the curable compositionto form a pressure sensitive adhesive.
 10. The method of claim 9,wherein the X-A-B-A-X reactive oligomer is the reaction product of aHO—B—OH hydroxyl-capped prepolymer and an X—Z compound wherein Z is anisocyanate group and X is an ethylenically unsaturated group linked tothe Z group.
 11. The method of claim 9, wherein the adhesive comprises aself-wetting and removable adhesive.
 12. The method of claim 9, whereinthe adhesive comprises an optically clear adhesive.
 13. An adhesivearticle comprising: a pressure sensitive adhesive comprising: the curedreaction product of at least one X-A-B-A-X reactive oligomer, wherein Xcomprises an ethylenically unsaturated group, B comprises a non-siliconeunit with a number average molecular weight of 5,000 grams/mole orgreater, and A comprises a urethane linking group, wherein the adhesiveis self wetting and removable; and a substrate.
 14. The adhesive articleof claim 13, wherein the substrate is a tape backing, a film, a sheet,or a release liner.
 15. The adhesive article of claim 14, whereinadhesive is optically clear.
 16. The adhesive article of claim 15,wherein the substrate comprises a film wherein the film comprises anoptically active film comprising a visible mirror film, a color mirrorfilm, a solar reflective film, a diffusive film, an infrared reflectivefilm, an ultraviolet reflective film, a brightness enhancement film, adual brightness enhancement film, an absorptive polarizer film, anoptically clear film, a tinted film, a privacy film, a light-collimatingfilm, or an antireflective film.
 17. The adhesive article of claim 13,wherein B comprises an oxyalkylene group.
 18. The adhesive article ofclaim 13, further comprising a second substrate, wherein the secondsubstrate comprises a rigid surface, a flexible surface, a tape backing,a film, a sheet, or a release liner.
 19. The adhesive article of claim13, wherein the pressure sensitive adhesive further comprises at leastone additive, wherein the additive comprises a pressure sensitiveadhesive, a plasticizing agent, a tackifying agent or a mixture thereof.20. The adhesive article of claim 19, comprising 5-60 weight % of addedpressure sensitive adhesive and 5-55 weight % plasticizer.
 21. Theadhesive article of claim 19, wherein the plasticizer comprisesisopropyl myristate or polypropylene glygol.
 22. The adhesive article ofclaim 19, wherein the added pressure sensitive adhesive comprises a(meth)acrylate pressure sensitive adhesive.
 23. The adhesive article ofclaim 19, wherein the added pressure sensitive adhesive comprises anacid-containing (meth)acrylate pressure sensitive adhesive.